With gas prices (and futures) priced where they are, it would be very hard to make the case anywhere in the country that building a new coal plant is economic. Many big utilities (e.g. AEP and FirstEnergy) are retiring many coal plants--they're too costly to operate, compared to cheaper power from gas plants, and the thin profit margins don't support the capital upgrades that would be needed to meet environmental regulations. Of course, gas prices may move up, but with 44% of our electricity already coming from coal, it's hard to make the case that building more coal is "diversifying the portfolio."

Coal plants also have the problem that they operate with less flexibility than gas-fired plants. As more variable energy resources (==renewables like wind and solar) come on-line, that flexibility is an important factor in evaluating what new power plants to build. E.g., the California system operator has started a major stakeholder process to consider options for ensuring sufficient flexible resources to accommodate the high RPS standards in the state.